Method for fabricating BOC semiconductor package

Abstract

A BOC (board-on-chip) semiconductor package includes a semiconductor die having die contacts, a substrate bonded circuit side down to the die, and an adhesive layer bonding the substrate to the die. The substrate includes a circuit side having a pattern of conductors and wire bonding sites, and a back side having an array of external contacts (e.g., BGA solder balls) in electrical communication with the conductors. The bonding sites on the conductors overhang the peripheral edges of the substrate such that access is provided for bonding wires to the bonding sites and to the die contacts. Because the substrate is bonded circuit side down to the die, a loop height of the wires, and an overall height (profile) of the package are reduced by a thickness of the substrate. In addition, a planarity of molded segments that encapsulate the wires is improved, and mold bleed during molding of the molded segments is reduced. A method for fabricating the BOC package includes the steps of: providing the die with the die contacts, providing the substrate with the conductors and the overhanging wire bonding sites on the circuit side and external contacts on the back side, bonding the substrate circuit side down to the die, wire bonding the wires to the wire bonding sites and to the die contacts, and then forming the molded segments to encapsulate the wires.

What is claimed is:  
     
       1. A method for fabricating a semiconductor package comprising: 
       providing a semiconductor die;  
       providing a substrate having a first side, an opposing second side and an edge, the substrate comprising a plurality of conductors on the first side having surfaces, opposing surfaces, portions overhanging the edge, and bonding sites on the opposing surfaces on the portions;  
       forming an adhesive layer in contact with the first side, the surfaces, and the portions to attach the substrate to the die with the first side acing towards the die and the second side facing away from the die; and  
       bonding a plurality of wires to the bonding sites and to the die.  
     
     
       2. The method of  claim 1  further comprising forming a plurality of external contacts on the second side in electrical communication with the conductors and encapsulating the wires in an encapsulant. 
     
     
       3. The method of  claim 1  further comprising forming a mask on the second side having a plurality of openings and forming a plurality of terminal contacts in the openings in electrical communication with the conductors. 
     
     
       4. The method of  claim 1  wherein the adhesive layer comprises tape or a cured polymer. 
     
     
       5. The method of  claim 1  wherein the substrate comprises a polymer resin and glass fibers. 
     
     
       6. A method for fabricating a semiconductor package comprising: 
       providing a semiconductor die comprising a circuit side, an edge and a plurality of die contacts on the circuit side;  
       providing a substrate having a first side and a second side, the substrate comprising a plurality of conductors on the first side, a plurality of bonding sites proximate to the first side comprising portions of the conductors extending from the edge, and a plurality of external contacts on the second side in electrical communication with the conductors, the conductors having surfaces and opposing surfaces on the portions wherein the bonding sites are located;  
       forming an adhesive layer between the first side and the circuit side in contact with the surfaces and supporting the portions; and  
       bonding a plurality of wires to the bonding sites and to the die contacts.  
     
     
       7. The method of  claim 6  further comprising encapsulating the wires and at least some of the substrate and the die in an encapsulant to form molded segments. 
     
     
       8. The method of  claim 6  wherein the adhesive layer has a peripheral shape larger than that of the substrate. 
     
     
       9. The method of  claim 6  wherein the external contacts comprise balls in a ball grid array. 
     
     
       10. The method of  claim 6  wherein the substrate comprises a plurality of second bonding sites on the second side in a grid array in electrical communication with the conductors and configured to attach the external contacts to the substrate. 
     
     
       11. The method of  claim 6  wherein the adhesive layer comprises tape or a cured polymer. 
     
     
       12. A method for fabricating a board-on-chip semiconductor package comprising: 
       providing a semiconductor die comprising a face and a plurality of die contacts on the face;  
       providing a substrate comprising a circuit side, a back side, an edge, a plurality of conductors on the circuit side having surfaces and opposing surfaces, and a plurality of bonding sites on the opposing surfaces comprising portions of the conductors overhanging the edge;  
       forming an adhesive layer between the circuit side and the face in contact with the surfaces;  
       wire bonding a plurality of wires to the bonding sites and to the die contacts;  
       encapsulating the wires in an encapsulant; and  
       forming a plurality of external contacts on the back side of the substrate in electrical communication with the conductors.  
     
     
       13. The method of  claim 12  wherein the encapsulating step comprises forming molded segments on the die and the edge of the substrate. 
     
     
       14. The method of  claim 12  wherein the external contacts comprise balls in a ball grid array. 
     
     
       15. The method of  claim 12  further comprising forming a solder mask on the back side of the substrate having a plurality of openings for the external contacts. 
     
     
       16. The method of  claim 12  wherein the substrate comprises a material selected from the group consisting of bismaleimide-trizine (BT), epoxy, and polyimide. 
     
     
       17. The method of  claim 12  wherein the adhesive layer comprises tape or a cured polymer. 
     
     
       18. A method for fabricating a semiconductor package comprising: 
       providing a semiconductor die comprising a face and a plurality of die contacts on the face;  
       providing a substrate having an edge, a circuit side and a back side;  
       forming a plurality of conductors on the circuit side having surfaces and opposing surfaces, and a plurality of bonding sites on the opposing surfaces on portions of the conductors overhanging the edge;  
       forming a plurality of external contacts on the back side in electrical communication with the conductors;  
       forming an adhesive layer between the circuit side and the face in contact with the surfaces configured to attach the substrate to the die and to support the portions;  
       bonding a plurality of wires to the die contacts and to the bonding sites; and  
       molding an encapsulant to the die and to the substrate.  
     
     
       19. The method of  claim 18  wherein the forming the external contacts step comprises bonding or forming balls on the substrate. 
     
     
       20. The method of  claim 18  wherein the forming the adhesive layer step comprises attaching a polymer tape to the die or the substrate. 
     
     
       21. The method of  claim 18  wherein the forming the adhesive layer step comprises applying a curable polymer to the die or the substrate. 
     
     
       22. The method of  claim 18  further comprising forming a mask on the back side of the substrate having openings for the external contacts. 
     
     
       23. The method of  claim 18  wherein the substrate comprises a material selected from the group consisting of bismaleimide-trizine (BT), epoxy, and polyimide.